At least six people were killed and more than 15 injured on Thursday when a suspected Taliban suicide bomber rammed his motorcycle into a government bus in Rawalpindi, the military’s garrison city just outside Islamabad.

A senior police officer told Reuters that the bus was carrying workers from the Khan Research Laboratories, a nuclear facility, about an hour’s drive from Islamabad. Another police officer at the scene said a severed head was found which appeared to be that of the suicide bomber.